1. Field of the Invention
This invention relates to a modular light-weight building block, and a system and method for construction using a plurality of the blocks.
2. Description of the Relevant Art
Modular commercial and residential buildings often use pre-fabricated wall and roof units assembled at the site to form a building. This building system approach can reduce construction time and improve quality, but the additional costs of special materials, trained assemblers and special equipment may nullify cost savings.
The on-site construction of a building wall generally takes weeks or months and requires heavy equipment, and the services of many skilled trades. A larger number of workers can be committed to shorten the construction time, but quality and safety generally suffer.
Precast concrete tilt-up wall construction requires placement of units with heavy equipment and skilled labor. Prefabricated concrete walls can be quite large and cumbersome, with dimensions often exceeding 10 or 15 feet. Conventional concrete tilt-up panels have relatively low energy efficiency and require additional material and labor from other trades to insulate and finish.
Wall sandwich panels are another form of the prefabricated wall unit. Preformed wall sandwich panels have a rigid insulation core covered by wood, wood products, steel, or aluminum sheeting. Utility installation in sandwich panels is often difficult. Heavy equipment or a specialized crew is often required for placement, and the panels have a lower resistance to fire than masonry.
Other conventional forms of wall construction such as wood/steel stud framing and masonry require many skilled trades to complete multiple layers of structural and finish materials. This procedure is time and cost consuming since each trade must finish its task before the other can begin.
Conventional roof systems generally include a collection of planar trusses covered with panels of plywood or chipboard and finished with tar paper and shingles. Significant time is required to align the trusses, nail the panels, and apply the finish layer. Quality of workmanship often suffers from the large number of operations required to complete the work and the unstable platform on which the work must be performed.
Conventional pre-fabricated and site-constructed building systems have structural problems as well. Most wall systems have strong base units (blocks or panels), but deficiencies in the connections between units lead to a lack of structural continuity and a weak overall structure. For example, individual concrete masonry units have relatively high compressive strength, but the finished wall has poor resistance to shear and bending. Dimensioned lumber studs in conventional "stick" construction are individually strong in compression, tension, shear and bending; however connections between panels are often weak in tension and bending. Precast tilt-up panels are designed to withstand high loads on individual panels during shipment, but overall structural integrity is determined by the strength of field welds on connecting tabs, which may be compromised by poor alignment or faulty welding under adverse environmental conditions.
Conventional roofing systems also exhibit structural deficiencies. Roofing panels are normally nailed or stapled to 2".times.4" trusses. Resistance to uplift of the panels is limited by the shear forces between nails (or staples) and wood. Resistance to uplift and shear at the wall/roof interface is controlled by individual nails, staples, thin metal straps, and/or light metal connector plates. The wall/roof juncture often represents a weak link in the structural system.
The deficiencies of existing light construction systems become evident under two types of loads. First, slow settling or working of the foundation can introduce stress concentrations in the wall and at the wall/roof interface, eventually leading to shear failure with associated deformations. Severe dynamic loading, such as hurricanes, tornadoes, or earthquakes, can impose high level shear and bending loads on walls, leading to structural damage or collapse of the building. Alternately, the walls may remain intact while panels are pulled from the roof, or the entire roof may separate from the building and collapse on inhabitants.
In light of the short-comings of the existing techniques, new options have been developed in building construction to reduce cost, time, labor, and skill needed while increasing the reliability and quality of the finished product.
In order to minimize the amount of skill and labor required to assemble and finish a wall at the job site, small building blocks are often used. These blocks may be stacked adjacent to one another to form a wall. Generally, each block is made of an insulating foam material attached together with fasteners or rods placed between or within each block. The fasteners or rods are often placed through the insulating foam material securing each block to an adjacent block and to a foundation upon which the wall of blocks resides.
To provide proper coupling between blocks, the fasteners or rods may be aligned through conduits placed at the centerline of each block. The fasteners or rods are made of rigid material extending generally the height or width of each block. The irregular shape of some blocks causes problems in alignment of rigid fasteners or rods through the conduit to a point of affixation. Moreover, fasteners and rods are often placed through the block centerline and within the less dense foam insulating material thereby presenting a support framework which bears on material lacking proper internal support or rigidity. Compression forces acting at one or more stress points within the surrounding wall may cause distortion or buckling of the less dense insulating material, possibly leading to serious damage to the entire structure.
Another difficulty with conventional forms of building blocks is their inability to be quickly and simultaneously secured together using selective tensioning of the blocks to adjacent blocks between the roof and foundation of the ensuing building. Placement and coupling together of blocks to form a wall has been difficult due to the complications that can arise when the blocks are not properly constructed. Thus, while pre-fabricated blocks of smaller geometry may be preferable over pre-fabricated panels or entire walls, the internal structure and geometry of conventional blocks, and the shortcomings or coupling systems, make them non-suitable for permanent fixtures exposed to severe loading conditions.
Light-weight panels have also been developed for roofing systems. The panels often comprise a planar section of light-weight insulating material sandwiched between two pieces of plywood or other structural material. One major drawback of this system is compression and creep of the insulating material over time.